Method and system for television communication



April 3946. J. H. HOMR IGHOUS 2398,42 METHOD AND SYSTEM FOR TELEVISIONCOMMUNICATION Original Filed May 13. 1940 4 snags-sheet 1 Moo. POWER AMEAM]? osc. 7, ,BLANK- n FREQ.

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MOTOR April 16, 1946. i I H. HOMR|GHO U$ 2,393,542

METHOD AND SYSTEM FOR TELEVISION COMMUiiICATION I Ori inal Filed May is,1940 4 Sheets-Sheet 2 April 16, 1946. J. H. HOMRIGHOUS METHOD AND SYSTEMFOR TELEVISION COMMUNICATION 4 Sheets-Sheet 3 Original Filed May 13,1940 HALF WAVE

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FIGI5 April 1 1946- J. H. HOMRIGHOUS 8,

METHOD AND SYSTEM FOR TELEVISION COMMUNICATION Original Filed May 13,1940 4 Sheets-Sheet 4 Petente METHOD AND SYSTEM FOR TELEWSIQN comaCAEEQN John H. Homrighous, Oak Park, Ell.

()riginal application May 13, 1M0, Serial No. 33%,36d, new lfatent Rio.2,32il,699, dated dune l, 19%. Divided and this application September17, 19. .2, Serial No. 458.612

19 (Claims.

My invention relates to improvements in methocls and systems fortelevision communication and particularly to systems for producingsynchronizing signals for controlling and timing the various impulsesrequired for the production of a picture at both the transmitter andreceiver.

One of the objects of my invention is to provide an improved cathode raydeflecting system for producing interlace scanning by applying adifferent electrical condition to the vertical deflecting means inalternate fields or by changing the time interval of every other field.

Another object of my invention is to provide a synchronizing signalgenerating mechanism for producing the various impulses necessary forthe control of scanning in a cathode ray tube with provision foradjusting the speed of the mecha nism to develop substantially-widefrequency range of impulses. v j

Another object of my invention is the provision of synchronizing signalmechanism at the receiver which permits greater flexibility so that suchmechanism may respond to signals representing different picture ratesand also different number of lines per picture.

One of the main objects of my invention is an improved method ofalteringthe number of picture changes or frames in a given time in orderto televise motion picture film at 24 frames per second, or, thestandard for television practice of 30 frames per second, or at anyother desired number of frames per second.

Another object of my invention is the provision of a switching devicefor changing the number of horizontal lines per field or frame withoutchanging the frame frequency.

Another object of my invention is the provision of an element in thecathode-ray picture tube to initiate pulses of current to be used for.blanking purposes or for reducing the intensity of the electron beamduringthe retracing period or backward movement;

Another object of my invention is the provision of elements in thecathode-ray reproducing tube to initiate pulses of current to blank orreduce the intensity of the electron beam during the retracting period.

Another object of my invention is the provision of means forautomatically adjusting the lines horizontally in each image field.

Another object of my invention is the provision of means sensitive tovariations of lightin the reproduced images for controlling thebrightness of the images.

A feature of my invention is the generation of mission of this wave tothe receiver whereby the same wave form and frequency may be regeneratedand other frequencies may also be generated from the source of power atthe receiver. 1

Several methods for producing interlace scanning have been devised. Onesystem, known as the even line system, requires that the up and downmovements of the cathode ray be of unequal length, which has been verydifiicult to obtain. In my present invention, I have devised a morepositive method for developing control impulses siving alternate shortand long spaced periods of time. Another system, known as the odd linemethod, has been devised which requires a whole number of lines plus afraction of a line in each field so that the electron ray will start thesecond field at a fraction of a line distant from the start of the firstline in the first field. This system depends upon equal field length andexactly alike vertical deflecting means for all fields. In the preferredembodiment of my invention I employ different intervals to the vet-ti Ical deflecting means in alternate fields to shift the electron rayvertically the distance equal to the space of one horizontal line. Innone of the present systems can the number of pictures in a given timebe changed from 24 to 30 pictures to televise motion picture film at amuch lower rate, 24 frames per second, than the proposed standard ratefor television, 30 frames per second, as described further along. Noneof the above systems show elements added to the cathode-ray tubesto'initiate voltage pulses for blanking purposes. I

In my prior application Serial No. 306,537, filed November 28, 1939, thepicture signals are combined with control and sound or audio signals insuch a manner that all three are transmitted and reproduced as pictureor video signals.

According to a preferred embodiment of my present invention, a voltagewave at the frame frequency is generated at the transmitter, andcombined with the audio signals on a separate intermediate carrierfrequency, which in turn is modulated on the video carrier frequency andtransmitted by radio to the receiver.

Another advantage of my invention is the genoration of blanking pulsesby the pick up and viewing tubes, thereby eliminating the transmissionof these signals filtering equipment. I

Other objects, features and-advantages ofmy invention will appear fromtion taken in connection with the accompanying by radio and thenecessary.

thefollowinp descripdrawings, illustrating an embodiment thereof inwhich:

Figures 1 and 2 are simplified diagrammatic view of a televisiontransmittin station and a television receiving station, respectively,illustrating theprinciples applied in this invention.

Figure 3 is a motor driven device for generating control frequencies.

Figures 4 and 5 are end views of the disks shown in Figure 3 forgenerating the control or frame frequency.

Figure 14 shows an end view of disk used in Figure 13.

Figure 15 shows picture control character, reproduced at the receiver.

' Figure 16 shows my improved cathode-ray pick up tube with circuitconnections.

Figure 17 is a top view of the mosaic used in tube shown in Figure 17.

Figure 18 shows my improved cathode-ray viewing tube with circuitconnections.

In Figure 1, the numeral i designates a cathode-ray pick up tube of theconventional type and is known as an Iconoscope." It is to be understoodthat other tubes such as Orthiconoscope developed for perpendicularscanning'of all points on the mosaic, or the tube known as the imagedissector may be used instead of the one illustrated. As shown, the tubecomprises a mosaic, photoelectric screen on which a li ht image of theobject is projected and produced, having two metallic plates on theopposite side, and an electron gun for generating a rayof electronsdirected at the screen, and two sets of deflecting plates fordefiectingthe electron ray at the'line and field frequencies, so that itis caused to scan the screen. The picture and certain other controlcharacters are thereby developed and fed from one of the metallic platesby an output connector 2 to a modulating amplifier 3. The otherconnector 4 leads to a blanking pulse circuit 5 to be further describedin connection with' Figure 12. v

A carrier wave is provided by an oscillator 6 in the power amplifier 'l.Thisvcarrier now is modulated by the frequency band video or picturesignals through the modulation amplifier 3. The signals from theamplifier I are supplied by a connection 8 to the mixing circuit 3.Certain control signals are also transmitted as video signa1s.-

The numeral l0 designates a generator for producing pulsating voltagewaves or waves of sine form for controlling the sweep frequencies at thedesired frame frequency. The low frequency sweep control voltage wavesor signals through the medium oi amplifier ii, modulates another carrierproduced by oscillator i2 in its amplifier. stage l3.

The audio or sound signals from the microphone I4 are passed through anamplifier IS.

The sweep control signals and the audio s18- nalsare applied through a.mixer circuit ii to modulate a second main carrier wave in the poweramplifier stage II produced by the oscillator iii. The signals from theamplifier H are fed The two carrier waves, one, modulated by sweep Ifrequency control signals and audio signals, the other, modulated byvideo signals are mixed in the mixer circuit 9 and fed to the commonantenna 23 for transmission by radio.

The sweep control signals are transmitted in the form of sine waves,which are used to synchronize or control the scanning action with thetransmitter.

The antenna 2i receives the combined carrier signals from thetransmitter antenna 20 to a radio frequency amplifier 22, an oscillatorit reacts with these signals in the first stage 24 on thesuperheterodyne principle, to produce two intermediate-frequency signalswhich are fed to the two stages 25 and 26.

After suitable amplification, the video signals are detected at 21 andfed by a connection 23 to a reproducing device 29. The device 2! isrepresented as being in the form of a cathode-ray tube of well knownconstruction, and comprises a fluorescent screen, an. electron gun fordeveloping a ray of electrons directed toward the screen, and two setsof electrostatic plates for deflecting the electron ray at the line andfield frequencies to cause it to scan the screen. It is to be un- 26which contains the sweep signals and the audio signals and through theaction ofwthe second detector 30 the output of which goes to twoselective filters 3| and 32. The low frequency sweep control signalsafter leaving the filter 3|, still in modulated form on a carrier aredemodulated at 33 and fed to the frequency generator 34 where thesignals may be amplified and operate a signal generator to redevelopcontrol signals, or the signals may be used after suitable amplificationto directly control the scanning action at the receiver which will beexplained in more detail later.

The audio signal from the filter 32 is fed to the loud speaker 35. Thenumeral 36 represents what may becalled an automatic brightness controlcircuit and derives its energy from the changes in brightness of a spotor mark 31 televised from the transmitting tube and directed into aphotocell circuit. The output from this circuit is used to adjust thebias on previous stages to aid in maintaining the brightness of thereproduced picture substantially constant.

Referring to Figure 3, the numeral 33 represents a motor which isoperated from the local suppLv current and normally runs at approxi- Ymately 1800 R. P. M. Operated from the motor to the mixer circuit 9through the conductor I3. The revolving and stationary members are bet-The video si ter shown in Figures 4 and 5. In Figure 4 the disk 52 ismade up of two halves of polarizing material: each half may be rotatedthrough a very small angle and as shown on the drawing the planes ofpolarization are not parallel. This angle depending upon the desiredsize of the dark portion 49 or the period of the gap between pairs ofpulses as illustrated at 50.

From the above it will be seen that when the disk 42 is rotated past thestationary member 45 and between its source of light 48 andphotoelectric cell I that the intensity of the light reaching thephoto-cell will vary from zero to maximum value and back to zero whenrotated through aproximately 180 degrees.

Referring to Figure 5, the numeral M represents a disk of lightpolarizing material having a certain part painted or blacked out so thatrotating it in a clockwise direction past its stationary polarizedmember 43 and 44 and between its sources of light 46 and 41 and theirrespective shown in Figure 3. These photo-cells control the photocells52 and 58 the intensity of light reach-) ing each photo-cell will varyfrom zero value to maximum value and back to. zero during one half of arevolution and during the other half of the revolution there will be nolight change.

A system for producing the'proper sweep voltages and control signals isshown in'Figures 8 to 12 inclusive. In Figure 8 I have shown a photocell54 which may be the photo-cell 5| in Figure 3. This cell is responsiveto the variations of light intensity caused by the rotation of disk 42previously explained to cause grid excitationof amplifier 55. The anodeof tube 55 is connected through the primary winding 56 of a transformerto the positive-terminal of the voltage divider 51 to thereby producepulsating voltages for. controlling the discharge tube. To produce thedesired output wave of saw tooth form for field scanning I employ a gridcontrolled discharge tube circuit shown in Figure 9, where the pulsatingvoltages from transformer winding '56 are induced into the transformersecondary winding to drive the grid of tube 58 positive, discharging thecondenser 59 through the tube 58. Thus by alternately charging thecondenser 59 through the resistance 50 and discharging it through thetube 58 a saw tooth voltage is generated.- The vertical sweep. pulsesgenerated :by the wave forming circuits Figure 9 is fed to conductor 6|at the transmitting tube Figure 1 and as diagrammatically shown inFigure 6. The circuit of Fig ure 9 is also used to produce the linesweep voltages.

From the above description it will be seen that each revolution of thedisk 42 will produce two similar impulses in the transformer winding 58to trigger the discharge tube 58. The tube 58 may be biased so that onlythe positive pulses applied to the grid will operate the tube. Sincethere is a gap 49 in the disk 42 successive impulses will occur atdiflerently spaced intervals. Changing the speed of the disk by theadjustment of the cone pulley 89 will change the pic.- ture rate withoutchanging the number of lines per picture. a The control voltagesproduced in Figure 8 may be transmitted to the receiving station togovern the scanning thereat.

The pulses generated bythe disk 42 can be used to produce the linescanning control pulses by interposing frequency multipliers between thecircuits of Figures 8 and 9. I may also use disk 4| having associatedwith it two sources of light 46 and 41 and their respective photo-cells52 and light intensity caused by the rotation of the disk 4| aspreviously explained.

Referring to Figure 11, I have shown a circuit for producing analternating current from the variation. of light occurring in thephoto-cells 62 and 63 which may be the photo-cells 52 and 53 former 69to the positive side of voltage divider 10. The cathodes Hare connectedin parallel to an intermediate point of the voltage divider Ill. Thecathode 13 of photo-cell 62 is connected to the grid 64 of amplifier 56and through re-' sistance 14 to negative potential at the voltagedivider, thereby maintaining the grid 66 at a negative potential withrespect to cathode H and plate 68; the circuit is so arranged that anincrease in the intensity of light on the photo-cell 62 will increasethe current of tube 66. The photo-cell 63 has its anode 15 connected tothe grid 65 of amplifier tube -6 and it is maintained at a positivepotential with respect to its cathode 16. This causes a decrease inthe-current of tube 61 upon increasing the intensity of light directedtoward the photo-cell 53. Other amplifier tubes may be connected inparallel to increase the amplification.

Therefore, since the plates of tubes 56 and 61 are in parallel, therotation of, the disk 4| will alternately operate the photo-cells 62 and63 to produce continuous rising and falling current in the transformerprimary winding 69, whereby, alternating voltages are induced in thesecondary winding. These control voltages from winding 69 may be inducedinto the transformer winding of Figure 9 to control the verticaldeflection,

and by changing the speed of rotation of the disk 4| the duration of thetime per field is changed so that any desired number of frames persecond may be produced.

One method or system for producing interlace' scanning uses the disk 4|,Figure 5 with Figure 11, to develop impulses/to trigger the sweepgenerator, Figure 9, to thereby control the vertical reciprocatingmovement of the electron ray at different time intervals whereby onefield period will be of a, greater duration than the next succeedingfield since the dark portion on disk 4| extends through more than andegree are. Therefore, the return trace time in alternate fields will begreater than in the intervening fields, causing a fractional part of aline to be included in each field, which will have the efiect of placingthe lines of alternate fields between those of intervening fields.

From the above it will be seen that I have devised a novel method ofproducing unequal field constitute the frequency generator shown at It,I

Figure 1.

It is proposed to use frequency multiplying circuits for the purpose ofproducing the high frequency required for horizontal line scanning.

The field frequency is obtained as described above and from thesefrequencies the higher line fre-- quencies are produced.

Referring to Figure 10, two stages of frequency multiplication areshown. The secondary winding I8 is connected to the transformer winding88 in Figure 11 whichsupplles alternating pulses to the taped secondaryand in turn to the full wave rectifier tube I8 which delivers twice thenumber of pulses or cycles to the tuned filter comprising the condenser88 and the next transformer primary winding 8|. This double cycle signalis supplied by the taped secondary 82 to the full wave rectifier 83where it is again doubled and fed to the next succeedingtransformer-primary 84. The taped secondary 85 delivers alternatingcurrent to the next stage and so on until the desired high frequency forline scanning is obtained. While I have shown a circuit to double or tomultiply the frequencies, other frequency multiplying circuit may beused.

'In my invention I prefer to use the doublers and obtain 128 or 256lines per field, where each field will have exactly the same number ofpulses, therefore, the same number of lines for each field and to avoidinterference with local power, all that is necessary to do is to changeslightly the field rate, which will of course change the line frequencybut will not change the number of lines per field.

With reference to Figure 7, I have provided two switches 88 and 81 forshorting out one or more stages of doublers; for instance, certainstations could be operating on 256 lines per field and other stations on128 lines per field.

In order to produce or develop interlaced scanning from a sine formvoltage wave it is necessary to identify every other field pulse and insome manner cause the horizontal lines of one field to fall in betweenthe lines produced in the other field or the lines of one field are evennumbered and in the second field they are odd numbered. I-accomplishthese features by the circuit shown in Figure 12. In this circuit,voltage waves of sine form are supplied from the circuit,

of Figure 11 to a full wave rectifier 88 of conventional design, whichmay be one stage of Figure 10. The output wave form is shown at 81;these pulses are fed through the transformer winding 88, which may bethe winding 81 in Figure 10, to wave forming circuit Figure 9 to drivethe grid of tube 58 positive discharging the condenser 58, therebyproducing saw tooth form waves for vertical scanning as previouslydescribed. Inductively connected with the transformer winding 68 inFigure 11 is a half wave rectifier 88, the output wave form is shown at88.

The current in the half wave rectifier load can be adjusted to impressvoltage pulses on the grid of tube 8| out of phase with the voltagepulses developed in the full wave rectifier 86. The anode of amplifier8| is connected through the primary transformer winding 82 to battery.The current pulses in the primary winding 82 .will induce in thesecondary a voltage which will alter the potential in conductor 93, fromthat furnished by the battery, for the duration of each pulse and inphase with the vertical sawtooth voltage waves. The conductor 83supplies potential through a centering resistance to one verticaldeflecting plate. ing plate is supplied with potential from the samesource through another centering resistance not shown. The potential onthe plate of ampllfier 8| is adjustable, depending upon the spacebetween lines.

The rectifier and amplifier 8| will operate during each positive pulseto increase or decrease the potential on one of the deflecting plateswithout changing the potential on the opposite plates, which willhave'the effect of raising or lowering the horizontal lines.

From the above description it will be seen that I have provided a noveland very simple means for interlace scanning or for shifting theposition of the horizontal lines scanned .in a cathode-ray tube, duringalternate field pulses and which are controlled by the generator at thetransmitting station. Thus eliminating the necessity of transmitting byradio synchronizing pulses other than the one sine form wave. Y

At the receiver I employ thesame means for identifying the positivepulses and at the same time causing the shift in the position ofhorizontal lines on the viewing tube screen.

The circuit figure number shown inFigure 7, omitting Figure 11, mayconstitute in one receiving station the frequency generator shown at 34,Figure 2.

From the above description it will be seen that the line pulses aredefinitely locked with the field pulses, or in other words, the samepulse that triggers the vertical deflection also supplies throughmultiplying circuits the trigger pulses for line scanning.

Furthermore, from the above description, the control of the field andline deflecting circuits at the receiver from the sine form voltage wavetransmitted by radio from the transmitting station will cause thecathode-ray or electron ray at the viewing tube to be in exactsynchroniza tion with the cathode-ray in the pick up tube, whenever thereceiving station is tuned to the proper carrier wave.

In other words, at any time or interval that the I 48, than since asingle frequency or control volt-" age wave generated at the transmitterstation times the deflection of both the-field and the horizontal linesat both the transmitting station and reeciving station, the cathode-rayat the viewing tube would automatically be focused at the midpoint ofline 40 on the screen of the viewing tube, and furthermore since I haveprovided through the medium of a half wave rectifier, Figure 12, meansfor associating the positive pulse in each cycle of the control voltagewave with a certain field, the focused electron ray in each tube wouldalso fall in the proper field. The picture produced from this systemwill be approximately as' high as they are wide, since there isnonecessity of reserving space at the bottom of picture for synchronizingpulses.

The other vertical defiect- Another system for controlling the scanningoperations at the receiving station may comprise the motor 84, Figure13, having control circuits for keeping the position of the rotor instep with the alternating current signals. The motor 84 drives disks ormechanisms similar to those explained in connection with Figure 3 to inturn develop line and field trigger potentials, utilizing the circuitsshown in Figure 7. The motor and mechanism shown in Figure 13, togetherwith the circuits shown in Figure 7 may constitute the frequencygenerator 35, Figure 2, in another receiving station. The poweramplifier 85 may be supplied with signal current from the detector 33,Figure2. These signals, after proper amplification at 95, are fed to themotor 9t through contact 96 and 91. The half wave rectifier 98 willsupply the positive pulses to one winding of relay 99. The motor 9% issmall and carries a very light load; therefore very little power isrequired to operate it. Secured to its shaft are three disks ofpolarizing material, two of which are exactly like those shown inFigures 4 and with-their associated stationary polarized members andphoto-cells. The disks are designated by the same numbers M and t2 andoperate the circuits shown in-Figure 7, as previously explained, inconnection with the transmitting station. In the preferred embodiment ofmy invention I propose to substitute the disk ltd, Figure id, for thedisk H to thereby develop a series of trigger impulses having equallyspaced periods of time.

The third disk in Figure 13, designated we, and

like the viewlshown in Figure 14, is secured to the motor shaft in sucha manner that when it is rotated one half of a revolution to alter thelight in the photo-cell IIII (which may be substituted for thephoto-cell, Figure 8) to produce a pulse be considered in step with thepositive pulses of the sine form voltage wave supplied to the poweramplifier 95.

The relay 99 will not operate by separate pulse from either therectifier 98 or photo-cell Ilil. But since the motor is two pole, therotor may be out of step several degrees; in which case the relay wouldreceive aiding pulses from both the rectifier 98 and the photo-cell I0!and would operate to open its contacts at 97 which would include theresistance I02 in the motor circuit momentarily in order to slow itsspeed sufilciently over a few revolutions to slip the rotor back in stepwith the supply current.

From the above description it is shown that the disk secured to themotor shaft will automatically keep in step with the current supply andthat the other disk connected to the motor shaft will also generatevoltage waves and pulses of current in exact phase relation and insynchronism with the received signals.

This motor generator circuit or frecuency gencrating device, Figure 13,may be used to supply and to overcome this automatically Iihave provided a horizontal line m3, Figure 15, which is reproduced from thepermanent mark 37 at the transmitting tube Figure 1 and will occur inall picture changes and frames. From a point, just I at the left of thishorizontal mark I83, a ray of light is directed by mirror I06 andsuitable lenses to a photo-cell I85. This photo-cell may be used in thecircuit of Figure 8 which has been previously described. Thetransformenwinding 58 would be inductively connectedto the'winding I98,Figure 13, which winding is connected through the control relay I M. Themark will move to the left, should the motor speed lag the picture speedwhich will render relay Hll inopertronbeam will be reduced just at theright in i ative and give a slightly longer interval for the horizontallines. However, should the motor speed lead the picture time the markwould move to the right causing light to enter the photo-cell I05 whichwould operate relay I01 momentarily to include resistance I08 in themotor circuit, thereby reducing the speed of motor. This fea-' ture hasbeen disclosed in my prior application, referred to before.

The mark I03, Figure 15,. also 'serves another purpose, that is, itautomatically controls the, brightness of the picture reproduced by thereflections of the changes in the intensity of the line or mark I03 intothe photo-cell I09 from the mirror. The photo-cell I 09 may besubstituted for the one shown in Figure 8, whereby this circuit willfunction to adjust the bias on previous stages as shown in Figure 2 toassist in maintaining the brightness in the reproduced picturepractically constant.

With reference to Figure 16, I have shownmy improved pick up tube I,which improvement. consists in dividing the metallic plate on the backof the mosaic H0 into two parts III and H2, better shown in top viewFigure 17, with conductors extending from each metallic plate throughthe tube, the mosaic may be in two parts also, otherwise this pick uptube is of conventional design. Theconductor II3 extending from thesmaller of the two plates III which is located on the left side of"'thetube facing the front, controls the grid excitation of grid H6 ofamplifier tube H5.

The anode of tube H5 isconnected through primary winding 'IIS'of atransformer to positive battery.

the mosaic H0 when scanning the image it will at the end of eachscanning line he focused on a vertical image of full height of. thepicture caused by a narrow permanent flat bar I I1, shown outside thelens system in Figure 1. This mark will appear in all the fields, sothat each time the scanning beam reaches this vertical image a small.potential change will be produced in the grid I Id of theamplifier H5,which may be further amplified in other stages to in turn produce apulse of current in the primary transformer winding H6 which is inducedinto the secondary transformer winding lit to change the potential onthe'vcontrol grid H9 to reduce the intensity of the electron ray duringthe retrace period which is commonly known as blanking. These pulses,before being applied to the control grid may be slightly delayed by wellknown pulse delaying methods so that the intensity of the elecstant.' 5

With reference to Figure 18, I have shown a very similar arrangement tothat shown in'Figure 16 for blanking the electronray in the viewing tubeat the-receiver.

The element I 20 On the inside of the viewing tube and near the rightedge'facing the front, is composed of two metallic plates I2I and I22separated by insulating material l23. From the plate I2I a lead I25 isbrought out from the vacuum tube29 and extends to the grid I 25 of tubeI26 which is a similar circuit to that shown and explained in connectionwith Figure 16, and as thej 'i' electron ray contacts the plate I22, atthe end of each scanning line a potential change is produced on plateI2I for changing the potential of the control grid I21 after properamplification and as explained for the pick up tube. Thus at the end ofeach horizontal line the intensit of -ment for blanking the electronray-in pick up and viewing tubes during the vertical and horizontal lineretrace. will be understood that numerous modiflcations are possiblewithout departing from the spirit of my invention or the scope oi theclaims. This application is a division of application Serial Number334,864, filed May 13, 1940, and now Patent Number 2,320,699, issuedJune 1, 1943. Having thus described my invention, I claim: 1. In atelevision system, a cathode ray camera tube having an image plate andan electron ray directed toward the image plate, a motor, means formoving the said electron ray forward and backward horizontally andvertically to scan the said image plate, including variable speedmechanism driven by said motor, said mechanism provided with apparatusand suitable circuits forv of intercepted light beams, photo electricdevices having suitable circuit arrangements actuated by the saidintercepted light beams to develop impulses of current from a source ofdirect current in synchronism with the positive polarity pulses of thereceived alternating current signals, said impulses of current developedfrom the source of direct current for controlling the movement of theelectron ray in vertical directions during spaced periods of time, andfor controlling the electron ray to scan horizontal lines during each ofthe said periods to produce successive images from received picturesignals, and means for developing intervals of longer duration inalternate vertical periods to scan even line locations on said imageplate during the alternate periods and to scan odd line locations onsaid image plate during the intervening periods.

6. The system, in accordance with claim 5, in which there is providedswitching means to vary the number of line locations that may beperiods.

developing horizontal control signals, and verti- I image plate, wherebyeven line locations on the said image plate are scanned during alternateperiods and odd line locations on said image plate are scanned duringthe intervening periods.

2. The system, in accordance with claim 1, in which there is providedmeans for changing the speed of said mechanism to thereby change thenumber of times that the said image plate may be scanned during acertain interval.

3. In a television system, a cathode ray viewing tube provided with animage screen and an electron ray directed toward the image screen, a motor arranged to be driven by received synchronizing signals, meansincluding variable speed mechanism driven b said motor for moving the asaid electron ray forward andbackward horizontally and vertically overthe said image screen to produce successive images from received picturesignals, said mechanism provided with ap- Daratus and suitable circuitsfor producing horizontal control signals, and vertical control signalshaving alternately short and long periods of time between signals, meansactuated bysaid horizontal signals for immediately stopping the forwardhorizontal deflection of said ray, and means actuated by the saidvertical signals for stopping the forward vertical deflection of saidray at different locations on said image screen 'to scan even linelocations on said image plate during the alternate periods, and to scanodd line locations on said image plate during the intervening periods.

4. The system, in accordance with claim 3, in which there is providedmeans for changing the speed of said mechanism to thereby change thenumber of times that the said image plate may be scanned during acertain interval.

5. In a television system, a cathode ray viewing tube provided with animage screen and an electron ray directed toward the image screen,

a motor arranged to be driven by alternating current signals modulatedon a carrier, rotar light valves driven by said motor to vary the intensy 7. The system, in accordance with claim 5, in which there is a markincluded in said images, and means sensitive to variations in light fromthe mark to maintain the brightness of the reproduced imagessubstantially constant.

' 8. The system, in accordance with claim 1, in which there is providedmeans including a part oi said image plate to control the intensity ofthe said electron ray during its backward movement.

9. In a television receiver, a cathode ray tube having an image screenand an electron ray directed toward the screen, means for deflecting thesaid ray forward and backward to scan lines in successive fields on saidscreen, means for intercepting incoming control signals, means forstopping the forward deflection of the electron ray from any locationthat it has reached on said screen upon the reception of any of the saidsignals, and means for causing the electron ray to scan lines on saidscreen in one fleld different than the lines scanned in the previousfield under the control of said signals.

10. In a television receiver, a cathode ray viewing tube having an imagescreen and an electron ray directed toward the screen, means fordefleeting the said ray forward and backward vertically to scan linelocations in successive image frames, means for intercepting incomingcontrol impulses, and means for starting the backward deflection of theelectron ray from any location that it has reached on said screen uponthe reception of any one of the said impulses, and means for causing theelectron ray to scan odd and even lines in alternate and intermediateflelds respectively under .the control of said impulses.

11. In a television system, a cathode, ray tube having an image screenand an electron ray directed toward the image screen, means fordefleeting the said electron ray forward and backward to scan diflerentline locations on said screen, means including apparatus and suitablecircuits for developing control signals, means actuated solely by thesaid signals for stopping the forward deflection of said ray, and meansincluding switches for controlling the frequency of occurrence of saidsignals, thereby adjusting the number of line locations that may bescanned on said image screen.

12. In a television system, a cathode ray tube ward to scan diiierentline locations on said screen, a signal generator provided with suitablecircuitsfor producing control signals, means re sponsive to each of thesaid control signals for. immediately starting the backward deflectionof said ray, and manually controlled switches for changing the frequencyof occurrence of said signals, thereby adjusting the number of line 10cations that may ce scanned on said image screen.

13. In a television transmitter, a cathode ray camera tube having ascreen and an electron ray directed toward the screen, means fordeflecting the electron ray forward to scan line locations in successivefields on said screen, means for pro clucing control impulses, means fordeflecting the electron ray backward under the control of said impulses,means for causing the electron ray to scan lines on said screen in onefield difierent from the lines scanned in the previous field under thecontrol of said impulses, and means for changing the frequency ofoccurrence of said impulses to change thereby the number of deflectionsin a iven time.

14. In a television transmitter, a cathode ray camera tube havingascreen and an electron ray directed toward the screen, means fordeflecting the said ray forward during frame periods to scan linelocations in successive fields on the said screen, means for producingcontrol impulses,

means for deflecting the electron ray backward under the control of saidimpulses, means for causing the electron ray to scan odd and even linesin alternate and intermediate fields respecn tively under the control ofsaid impulses, and

rneans for changing the frequenc of occurrence of said impulses tochange thereby the number of frames scanned in a given time.

15. In a television system; a cathode ray tube having an image screenand an electron ray directed toward the image screen, means for defleeting the electron ray forward and backward to scan said screen toproduce thereon images from received signals, image means for controlling the intensity of the electron ray during the forward deflections tomaintainthe brightness of id. in a television system, a cathode ray tubehaving an image screen and an electron ray directed toward the imagescreen, means for del tingv the electron ray rorwarol and backward bothvertically and. horizontally to scan difierent line locations on saidscreen to produce thereon images from received signals, means forcontrolling the intensity of the electron ray during the iorwarddeflections to maintain the brightness oi the said images substantiallyconstant, and image means for controlling the deflecting means toadjustthe lines on said screen.

17. In a television receiver, a cathode ray tube havins a screen and anelectron ray directed toward the screen, means for deflecting theelectron raviortvard to scan said screen, means for producing controlimpulses in timed relation to received signals, meansior deflecting theelectron ray backward under the control oi said impulses, and meansresponsive to changes in irequency of occurrence of the received signalsfor automatically changing-the frequency of occurrence of the saidimpulses to change the number of deflections in a given time.

is. A. television receiver, in accordance with claim ll in which thereis provided means for adjusting said deflecting means to changetheveiocity or the-electron ray over said screen to change thereby the fullforward deflection time to equal the interval between said impulses,

19. The method of producing images from recelved video signalsandcontrol signals, comnrisinc picture images from said video signalsduring trace periods in reciprocating scanning actions, developing thereceived control signals to reverse the scanning actions and to causethe electron ray to scan difierent line. locations in alternate andintermediate periods, and utilizing image eiiects to maintain thebrilliancy of the reproduced

